No problem.  Clift is very nice place - one of the better hotels in the Union Square area.  I've stayed there a few times either with a provider (o/nite) or with provider visits.  Never a problem - no one cares.  Best to have her call and confirm before hand or on the way and give her your room no or call her and give it to her.  She can come right up - no one will check or even glance at something like that.  Also, I've never had a problem with the provider using the valet parking (a must do at the Clift).  Just tell the guy she's there to visit a friend and have it charged to your room.  (At least that's what I do - take care of the girls expenses!)  Good luck.